The omega-3 fatty acids found in fish may reduce your risk of stroke, but supplements won't help.
Most people don't eat much fish, unless it is smothered in batter and comes with chips. The National Diet Nutrition survey found that, on average, we eat less than the recommended one portion a week of oily fish (salmon, tuna, trout), the type with the most health benefit.
But the advantages of eating oily fish, thought to be due to their omega-3 fatty acids, are by no means conclusive. A review of the evidence in 2009 by the Cochrane Collaboration, which reviews results of all relevant good-quality studies, found no clear evidence that omega-3 fats reduce the incidence of strokes, heart attacks and cancers in either the general population or those at risk of heart problems.
Last week, the BMJ published research that found eating oily fish two to four times a week may reduce your risk of a stroke by 6%. But if you don't like fish, fish oil supplements are no substitute. The study (which added up results from the largest number of studies on fish oils and strokes so far), showed they had no benefit.
So is this enough to convince you to eat more oily fish? Or are you more likely to avoid strokes and heart attacks through regular exercise, eating a healthy (low-fat, high-fibre) diet, not smoking and sticking to recommended levels of alcohol consumption?
The study showed that those who ate fish five times a week had a 12% reduction in stroke risk. However, the authors say their research can't show for sure that this is linked to eating fish. People who eat more fish may be healthier anyway, and it is hard for studies to take into account all the ways in which they may be different from other people - for example, they may also eat less meat and exercise more.
The researchers are clear, however, that supplements don't do as good a job as whole foods, something other studies have found too. Oily fish also contains vitamins D and B and amino acids, which might be needed to work with the omega-3 fatty acids to reduce the risk of stroke. You may need all the constituents of a food for it to be good for you.
Fish oil has excited many research groups who have looked at its benefits in reducing asthma symptoms (based on the hypothesis that Inuits eat lots of oily fish and don't get asthma), relieving Crohn's disease, stopping weight loss in people with cancer and improving the symptoms of schizophrenia. None of the studies found that fish oil works, although most tested supplements instead of omega-3 fatty acids in whole foods.
Since we eat more red meat than fish it wouldn't hurt to redress the balance. The mechanism by which it is meant to reduce strokes and heart attacks is unclear, but omega-3 fatty acids are thought to reduce triglyceride fats, reduce inflammation and blood clotting. We can't make our own omega-3 fatty acids so a bit more oily fish, rather than supplements, would probably be good for most of us.
Will fish oil supplements make you healthier? Photograph: TS Photography/Getty Images